diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ha/HAServiceProtocol.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ha/HAServiceProtocol.java
index 85912c7c76f..57eee187b0e 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ha/HAServiceProtocol.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ha/HAServiceProtocol.java
@@ -20,6 +20,7 @@ package org.apache.hadoop.ha;
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
 import org.apache.hadoop.fs.CommonConfigurationKeys;
+import org.apache.hadoop.io.retry.Idempotent;
 import org.apache.hadoop.security.AccessControlException;
 import org.apache.hadoop.security.KerberosInfo;
 
@@ -106,6 +107,7 @@ public interface HAServiceProtocol {
    * @throws IOException
    *           if other errors happen
    */
+  @Idempotent
   public void monitorHealth() throws HealthCheckFailedException,
                                      AccessControlException,
                                      IOException;
@@ -121,6 +123,7 @@ public interface HAServiceProtocol {
    * @throws IOException
    *           if other errors happen
    */
+  @Idempotent
   public void transitionToActive(StateChangeRequestInfo reqInfo)
                                    throws ServiceFailedException,
                                           AccessControlException,
@@ -137,6 +140,7 @@ public interface HAServiceProtocol {
    * @throws IOException
    *           if other errors happen
    */
+  @Idempotent
   public void transitionToStandby(StateChangeRequestInfo reqInfo)
                                     throws ServiceFailedException,
                                            AccessControlException,
@@ -153,6 +157,7 @@ public interface HAServiceProtocol {
    *           if other errors happen
    * @see HAServiceStatus
    */
+  @Idempotent
   public HAServiceStatus getServiceStatus() throws AccessControlException,
                                                    IOException;
 }
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/retry/AtMostOnce.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/retry/AtMostOnce.java
new file mode 100644
index 00000000000..624bb43ab7c
--- /dev/null
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/retry/AtMostOnce.java
@@ -0,0 +1,41 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.io.retry;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Inherited;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+import org.apache.hadoop.classification.InterfaceStability;
+
+/**
+ * Used to mark certain methods of an interface with at-most-once semantics.
+ * 
+ * Server must guarantee that methods are executed at most once, by keeping
+ * a retry cache. The previous response must be returned when duplicate 
+ * requests are received. Because of these guarantee, a client can retry
+ * this request on failover and other network failure conditions.
+ */
+@Inherited
+@Retention(RetentionPolicy.RUNTIME)
+@Target(ElementType.METHOD)
+@InterfaceStability.Evolving
+public @interface AtMostOnce {
+
+}
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/RefreshUserMappingsProtocol.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/RefreshUserMappingsProtocol.java
index b72e3ed6df7..005b2948ea2 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/RefreshUserMappingsProtocol.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/RefreshUserMappingsProtocol.java
@@ -22,6 +22,7 @@ import java.io.IOException;
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
 import org.apache.hadoop.fs.CommonConfigurationKeys;
+import org.apache.hadoop.io.retry.Idempotent;
 import org.apache.hadoop.security.KerberosInfo;
 
 /**
@@ -43,12 +44,13 @@ public interface RefreshUserMappingsProtocol {
    * Refresh user to group mappings.
    * @throws IOException
    */
+  @Idempotent
   public void refreshUserToGroupsMappings() throws IOException;
   
   /**
    * Refresh superuser proxy group list
    * @throws IOException
    */
-  public void refreshSuperUserGroupsConfiguration() 
-  throws IOException;
+  @Idempotent
+  public void refreshSuperUserGroupsConfiguration() throws IOException;
 }
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/authorize/RefreshAuthorizationPolicyProtocol.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/authorize/RefreshAuthorizationPolicyProtocol.java
index 4407a7e8e32..0f0b25d8344 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/authorize/RefreshAuthorizationPolicyProtocol.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/authorize/RefreshAuthorizationPolicyProtocol.java
@@ -22,6 +22,7 @@ import java.io.IOException;
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
 import org.apache.hadoop.fs.CommonConfigurationKeys;
+import org.apache.hadoop.io.retry.Idempotent;
 import org.apache.hadoop.security.KerberosInfo;
 
 /**
@@ -42,5 +43,6 @@ public interface RefreshAuthorizationPolicyProtocol {
    * Refresh the service-level authorization policy in-effect.
    * @throws IOException
    */
+  @Idempotent
   void refreshServiceAcl() throws IOException;
 }
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/tools/GetUserMappingsProtocol.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/tools/GetUserMappingsProtocol.java
index c0c107933f5..3e80ac030d3 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/tools/GetUserMappingsProtocol.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/tools/GetUserMappingsProtocol.java
@@ -21,6 +21,7 @@ import java.io.IOException;
 
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.io.retry.Idempotent;
 
 /**
  * Protocol implemented by the Name Node and Job Tracker which maps users to
@@ -41,5 +42,6 @@ public interface GetUserMappingsProtocol {
    * @return The set of groups the user belongs to.
    * @throws IOException
    */
+  @Idempotent
   public String[] getGroupsForUser(String user) throws IOException;
 }
diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
index 661d915b90d..f3938a76f50 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
@@ -335,6 +335,9 @@ Release 2.1.0-beta - 2013-07-02
     HDFS-4373. Add HTTP API for querying NameNode startup progress. (cnauroth)
 
     HDFS-4374. Display NameNode startup progress in UI. (cnauroth)
+
+    HDFS-4974. Add Idempotent and AtMostOnce annotations to namenode
+    protocol methods. (suresh)
     
   IMPROVEMENTS
 
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocol/ClientProtocol.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocol/ClientProtocol.java
index d77cde5819e..5789c3615eb 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocol/ClientProtocol.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocol/ClientProtocol.java
@@ -40,6 +40,7 @@ import org.apache.hadoop.hdfs.server.namenode.NotReplicatedYetException;
 import org.apache.hadoop.hdfs.server.namenode.SafeModeException;
 import org.apache.hadoop.io.EnumSetWritable;
 import org.apache.hadoop.io.Text;
+import org.apache.hadoop.io.retry.AtMostOnce;
 import org.apache.hadoop.io.retry.Idempotent;
 import org.apache.hadoop.security.AccessControlException;
 import org.apache.hadoop.security.KerberosInfo;
@@ -139,7 +140,7 @@ public interface ClientProtocol {
    * <p>
    * Blocks have a maximum size.  Clients that intend to create
    * multi-block files must also use 
-   * {@link #addBlock(String, String, ExtendedBlock, DatanodeInfo[])}
+   * {@link #addBlock}
    *
    * @param src path of the file being created.
    * @param masked masked permission.
@@ -170,7 +171,10 @@ public interface ClientProtocol {
    *
    * RuntimeExceptions:
    * @throws InvalidPathException Path <code>src</code> is invalid
+   * <p>
+   * <em>Note that create with {@link CreateFlag#OVERWRITE} is idempotent.</em>
    */
+  @AtMostOnce
   public HdfsFileStatus create(String src, FsPermission masked,
       String clientName, EnumSetWritable<CreateFlag> flag,
       boolean createParent, short replication, long blockSize)
@@ -204,6 +208,7 @@ public interface ClientProtocol {
    * RuntimeExceptions:
    * @throws UnsupportedOperationException if append is not supported
    */
+  @AtMostOnce
   public LocatedBlock append(String src, String clientName)
       throws AccessControlException, DSQuotaExceededException,
       FileNotFoundException, SafeModeException, UnresolvedLinkException,
@@ -409,6 +414,7 @@ public interface ClientProtocol {
    * @throws SnapshotAccessControlException if path is in RO snapshot
    * @throws IOException an I/O error occurred 
    */
+  @AtMostOnce
   public boolean rename(String src, String dst) 
       throws UnresolvedLinkException, SnapshotAccessControlException, IOException;
 
@@ -422,6 +428,7 @@ public interface ClientProtocol {
    *           contains a symlink
    * @throws SnapshotAccessControlException if path is in RO snapshot
    */
+  @AtMostOnce
   public void concat(String trg, String[] srcs) 
       throws IOException, UnresolvedLinkException, SnapshotAccessControlException;
 
@@ -460,6 +467,7 @@ public interface ClientProtocol {
    * @throws SnapshotAccessControlException if path is in RO snapshot
    * @throws IOException If an I/O error occurred
    */
+  @AtMostOnce
   public void rename2(String src, String dst, Options.Rename... options)
       throws AccessControlException, DSQuotaExceededException,
       FileAlreadyExistsException, FileNotFoundException,
@@ -484,6 +492,7 @@ public interface ClientProtocol {
    * @throws SnapshotAccessControlException if path is in RO snapshot
    * @throws IOException If an I/O error occurred
    */
+  @AtMostOnce
   public boolean delete(String src, boolean recursive)
       throws AccessControlException, FileNotFoundException, SafeModeException,
       UnresolvedLinkException, SnapshotAccessControlException, IOException;
@@ -704,6 +713,7 @@ public interface ClientProtocol {
    * @throws AccessControlException if the superuser privilege is violated.
    * @throws IOException if image creation failed.
    */
+  @AtMostOnce
   public void saveNamespace() throws AccessControlException, IOException;
 
   
@@ -725,6 +735,7 @@ public interface ClientProtocol {
    * 
    * @throws AccessControlException if the superuser privilege is violated.
    */
+  @Idempotent
   public boolean restoreFailedStorage(String arg) 
       throws AccessControlException, IOException;
 
@@ -732,6 +743,7 @@ public interface ClientProtocol {
    * Tells the namenode to reread the hosts and exclude files. 
    * @throws IOException
    */
+  @Idempotent
   public void refreshNodes() throws IOException;
 
   /**
@@ -741,6 +753,7 @@ public interface ClientProtocol {
    * 
    * @throws IOException
    */
+  @Idempotent
   public void finalizeUpgrade() throws IOException;
 
   /**
@@ -763,6 +776,7 @@ public interface ClientProtocol {
    *
    * @throws IOException
    */
+  @Idempotent
   public void metaSave(String filename) throws IOException;
 
   /**
@@ -918,6 +932,7 @@ public interface ClientProtocol {
    * @throws SnapshotAccessControlException if path is in RO snapshot
    * @throws IOException If an I/O error occurred
    */
+  @AtMostOnce
   public void createSymlink(String target, String link, FsPermission dirPerm,
       boolean createParent) throws AccessControlException,
       FileAlreadyExistsException, FileNotFoundException,
@@ -965,6 +980,7 @@ public interface ClientProtocol {
    * @param newNodes datanodes in the pipeline
    * @throws IOException if any error occurs
    */
+  @AtMostOnce
   public void updatePipeline(String clientName, ExtendedBlock oldBlock, 
       ExtendedBlock newBlock, DatanodeID[] newNodes)
       throws IOException;
@@ -997,6 +1013,7 @@ public interface ClientProtocol {
    * @param token delegation token
    * @throws IOException
    */
+  @Idempotent
   public void cancelDelegationToken(Token<DelegationTokenIdentifier> token)
       throws IOException;
   
@@ -1005,6 +1022,7 @@ public interface ClientProtocol {
    *         DataTransferProtocol to/from DataNodes.
    * @throws IOException
    */
+  @Idempotent
   public DataEncryptionKey getDataEncryptionKey() throws IOException;
   
   /**
@@ -1014,6 +1032,7 @@ public interface ClientProtocol {
    * @return the snapshot path.
    * @throws IOException
    */
+  @AtMostOnce
   public String createSnapshot(String snapshotRoot, String snapshotName)
       throws IOException;
 
@@ -1023,6 +1042,7 @@ public interface ClientProtocol {
    * @param snapshotName Name of the snapshot for the snapshottable directory
    * @throws IOException
    */
+  @AtMostOnce
   public void deleteSnapshot(String snapshotRoot, String snapshotName)
       throws IOException;
   
@@ -1033,6 +1053,7 @@ public interface ClientProtocol {
    * @param snapshotNewName new name of the snapshot
    * @throws IOException
    */
+  @AtMostOnce
   public void renameSnapshot(String snapshotRoot, String snapshotOldName,
       String snapshotNewName) throws IOException;
   
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocol/DatanodeProtocol.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocol/DatanodeProtocol.java
index 275b7c9a5c5..988590b5af4 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocol/DatanodeProtocol.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocol/DatanodeProtocol.java
@@ -25,6 +25,8 @@ import org.apache.hadoop.hdfs.DFSConfigKeys;
 import org.apache.hadoop.hdfs.protocol.DatanodeID;
 import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
 import org.apache.hadoop.hdfs.protocol.LocatedBlock;
+import org.apache.hadoop.io.retry.AtMostOnce;
+import org.apache.hadoop.io.retry.Idempotent;
 import org.apache.hadoop.security.KerberosInfo;
 
 /**********************************************************************
@@ -81,6 +83,7 @@ public interface DatanodeProtocol {
    * @return the given {@link org.apache.hadoop.hdfs.server.protocol.DatanodeRegistration} with
    *  updated registration information
    */
+  @Idempotent
   public DatanodeRegistration registerDatanode(DatanodeRegistration registration
       ) throws IOException;
   
@@ -98,6 +101,7 @@ public interface DatanodeProtocol {
    * @param failedVolumes number of failed volumes
    * @throws IOException on error
    */
+  @Idempotent
   public HeartbeatResponse sendHeartbeat(DatanodeRegistration registration,
                                        StorageReport[] reports,
                                        int xmitsInProgress,
@@ -120,6 +124,7 @@ public interface DatanodeProtocol {
    * @return - the next command for DN to process.
    * @throws IOException
    */
+  @Idempotent
   public DatanodeCommand blockReport(DatanodeRegistration registration,
       String poolId, StorageBlockReport[] reports) throws IOException;
     
@@ -133,6 +138,7 @@ public interface DatanodeProtocol {
    * writes a new Block here, or another DataNode copies a Block to
    * this DataNode, it will call blockReceived().
    */
+  @AtMostOnce
   public void blockReceivedAndDeleted(DatanodeRegistration registration,
                             String poolId,
                             StorageReceivedDeletedBlocks[] rcvdAndDeletedBlocks)
@@ -142,21 +148,25 @@ public interface DatanodeProtocol {
    * errorReport() tells the NameNode about something that has gone
    * awry.  Useful for debugging.
    */
+  @Idempotent
   public void errorReport(DatanodeRegistration registration,
                           int errorCode, 
                           String msg) throws IOException;
     
+  @Idempotent
   public NamespaceInfo versionRequest() throws IOException;
 
   /**
    * same as {@link org.apache.hadoop.hdfs.protocol.ClientProtocol#reportBadBlocks(LocatedBlock[])}
    * }
    */
+  @Idempotent
   public void reportBadBlocks(LocatedBlock[] blocks) throws IOException;
   
   /**
    * Commit block synchronization in lease recovery
    */
+  @AtMostOnce
   public void commitBlockSynchronization(ExtendedBlock block,
       long newgenerationstamp, long newlength,
       boolean closeFile, boolean deleteblock, DatanodeID[] newtargets,
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocol/NamenodeProtocol.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocol/NamenodeProtocol.java
index d9bae652b76..29bbb3b32a3 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocol/NamenodeProtocol.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocol/NamenodeProtocol.java
@@ -25,6 +25,8 @@ import org.apache.hadoop.hdfs.DFSConfigKeys;
 import org.apache.hadoop.hdfs.protocol.DatanodeInfo;
 import org.apache.hadoop.hdfs.security.token.block.ExportedBlockKeys;
 import org.apache.hadoop.hdfs.server.namenode.CheckpointSignature;
+import org.apache.hadoop.io.retry.AtMostOnce;
+import org.apache.hadoop.io.retry.Idempotent;
 import org.apache.hadoop.security.KerberosInfo;
 
 /*****************************************************************************
@@ -73,6 +75,7 @@ public interface NamenodeProtocol {
    * @throws IOException if size is less than or equal to 0 or
                                    datanode does not exist
    */
+  @Idempotent
   public BlocksWithLocations getBlocks(DatanodeInfo datanode, long size)
   throws IOException;
 
@@ -82,6 +85,7 @@ public interface NamenodeProtocol {
    * @return ExportedBlockKeys containing current block keys
    * @throws IOException 
    */
+  @Idempotent
   public ExportedBlockKeys getBlockKeys() throws IOException;
 
   /**
@@ -90,11 +94,13 @@ public interface NamenodeProtocol {
    * case of a non-active node.
    * @throws IOException
    */
+  @Idempotent
   public long getTransactionID() throws IOException;
 
   /**
    * Get the transaction ID of the most recent checkpoint.
    */
+  @Idempotent
   public long getMostRecentCheckpointTxId() throws IOException;
 
   /**
@@ -103,6 +109,7 @@ public interface NamenodeProtocol {
    * @throws IOException
    * @return a unique token to identify this transaction.
    */
+  @Idempotent
   public CheckpointSignature rollEditLog() throws IOException;
 
   /**
@@ -112,6 +119,7 @@ public interface NamenodeProtocol {
    *          of the name-node
    * @throws IOException
    */
+  @Idempotent
   public NamespaceInfo versionRequest() throws IOException;
 
   /**
@@ -124,6 +132,7 @@ public interface NamenodeProtocol {
    * @param msg free text description of the error
    * @throws IOException
    */
+  @Idempotent
   public void errorReport(NamenodeRegistration registration,
                           int errorCode, 
                           String msg) throws IOException;
@@ -134,6 +143,7 @@ public interface NamenodeProtocol {
    * @return  {@link NamenodeRegistration} of the node,
    *          which this node has just registered with.
    */
+  @Idempotent
   public NamenodeRegistration registerSubordinateNamenode(
       NamenodeRegistration registration) throws IOException;
 
@@ -151,6 +161,7 @@ public interface NamenodeProtocol {
    * @return {@link CheckpointCommand} if checkpoint is allowed.
    * @throws IOException
    */
+  @AtMostOnce
   public NamenodeCommand startCheckpoint(NamenodeRegistration registration)
   throws IOException;
 
@@ -162,6 +173,7 @@ public interface NamenodeProtocol {
    * @param sig {@code CheckpointSignature} which identifies the checkpoint.
    * @throws IOException
    */
+  @AtMostOnce
   public void endCheckpoint(NamenodeRegistration registration,
                             CheckpointSignature sig) throws IOException;
   
@@ -171,6 +183,7 @@ public interface NamenodeProtocol {
    * available to be fetched from the NameNode.
    * @param sinceTxId return only logs that contain transactions >= sinceTxId
    */
+  @Idempotent
   public RemoteEditLogManifest getEditLogManifest(long sinceTxId)
     throws IOException;
 }
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/protocol/TestAnnotations.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/protocol/TestAnnotations.java
new file mode 100644
index 00000000000..c461e2c8cfb
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/protocol/TestAnnotations.java
@@ -0,0 +1,43 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.protocol;
+
+import java.lang.reflect.Method;
+
+import org.apache.hadoop.hdfs.server.protocol.NamenodeProtocols;
+import org.apache.hadoop.io.retry.AtMostOnce;
+import org.apache.hadoop.io.retry.Idempotent;
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * Tests to make sure all the protocol class public methods have
+ * either {@link Idempotent} or {@link AtMostOnce} once annotations.
+ */
+public class TestAnnotations {
+  @Test
+  public void checkAnnotations() {
+    Method[] methods = NamenodeProtocols.class.getMethods();
+    for (Method m : methods) {
+      Assert.assertTrue(
+          "Idempotent or AtMostOnce annotation is not present " + m,
+          m.isAnnotationPresent(Idempotent.class)
+              || m.isAnnotationPresent(AtMostOnce.class));
+    }
+  }
+}